So if you're only roasting once or twice a year, we say skip buying a roasting pan and see if one of these alternatives will work for you instead. The big advantage of a roasting pan is that it's big, literally. A standard roasting pan can fit a 16-pound turkey with no problem. But many of us don't actually need to be roasting a 16-pound turkey, and a smaller turkey will fit quite easily in some of the cookware we already have.
The rule of thumb is that you want to be able to sit on your ball with your legs at a 90-degree angle or slightly more, but not less. Use these guidelines when you buy a fitness ball: If you are 4'11 - 5'4, get a ball that is 55cm. If you are 5'5 - 5'11, get a ball that is 65cm.
Inflate the ball to about 80% of diameter initially. Wait a further 24 hours before inflating to the recommended size. You should avoid using the ball within the first 24 hours. To gauge the correct size, place two boxes on the floor exactly the right distance apart using a tape measure. To test roll the ball between the boxes. When each end of the ball just touches both boxes you have the right size.